1. Field of the Invention
The present invention relates in general to control systems for controlling internal combustion engines, and more particularly, to control systems of a type which controls the fuel supply to the engine.
2. Description of the Prior Art
As is well known, when the engine is subjected to knocking, the output of the engine is lowered. Under this knocking condition, the con'rod bearings and main bearings are applied with abnormally high load due to the impactive pressure change in the cylinders. Furthermore, the knocking sometimes induces a seizure of pistons and valves due to high heat and pressure wave caused by the knocking.
In order to eliminate the problems caused by the knocking, various attempts have been hitherto made, which are, for example, delaying the ignition timing, enriching the air-fuel mixture and the like by sensing a high frequency vibration distinctively generated by the knocking. Some of these attempts are shown in Japanese Patent First Provisional Publications Nos. 63-97873 and 63-75354.
In addition to the knocking, "pre-ignition" is also the cause of lowering the output of the engine. As is known, the pre-ignition is an undesired phenomenon wherein due to a heat spot produced on an inner wall of a combustion chamber, the air-fuel mixture is overheated and thus ignited before the high tension ignition.
However, unlike knocking, in case of pre-ignition, the high frequency vibration is not produced. Thus, sensing the pre-ignition is much difficult as compared with sensing the knocking. Thus, hitherto, it has sometimes occurred that due to the pre-ignition, the durability of the engine is remarkably lowered.